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Retinal Arterioles (retinal + arteriole)

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Medical Sciences	100%

Selected Abstracts

Losartan and Ozagrel Reverse Retinal Arteriolar Constriction in Non-Obese Diabetic Mice

MICROCIRCULATION, Issue 5 2008
Seungjun Lee
ABSTRACT Objective: Reductions in retinal blood flow are observed early in diabetes. Venules may influence arteriolar constriction and flow; therefore, we hypothesized that diabetes would induce the constriction of arterioles that are in close proximity to venules, with the constriction mediated by thromboxane and angiotensin II. Methods: Using nonobese diabetic (NOD) mice, retinal measurements were performed three weeks following the age at which glucose levels exceeded 200 mg/dL, with accompanying experiments on age-matched normoglycemic NOD mice. The measurements included retinal arteriolar diameters and red blood cell velocities and were repeated following an injection of the thromboxane synthase inhibitor, ozagrel. Mice were subdivided into equal groups and given drinking water with or without the angiotensin II receptor antagonist, losartan. Results: Retinal arterioles were constricted in hyperglycemic mice, with a significant reduction in flow. However, not all arterioles were equally affected; the vasoconstriction was limited to arterioles that were in closer proximity to venules. The arteriolar vasoconstriction (mean arteriolar diameters = 51 ± 1 vs. 61 ± 1 , m in controls; p < 0.01) was eliminated by both ozagrel (61 ± 2 , m) and losartan (63 ± 2 , m). Conclusions: Venule-dependent arteriolar vasoconstriction in NOD mice is mediated by thromboxane and/or angiotensin II. [source]

Retinal arterioles have impaired reactivity to hyperoxia in type 1 diabetes

ACTA OPHTHALMOLOGICA, Issue 4 2010
Birgitte L. Justesen
Abstract. Purpose:, Diabetes has adverse effects on the retinal microvasculature. The purpose of this study was to compare the effects of inhalation of hypoxic, hyperoxic and normoxic,hypercapnic gas mixtures on retinal vessel diameter in people with and without diabetes. Methods:, Sixty-one participants (aged 24,50 years) 29 with (male : female ratio 2.6 : 1) and 32 without (male : female ratio 0.7 : 1) diabetes, inhaled hypoxic, hyperoxic and normoxic,hypercapnic gas mixtures for 3,5 mins. The diameters of arterioles and venules were measured using digital retinal images taken before and after gas inhalation. Results:, There was no significant difference in the diameters of arterioles and venules prior to gas inhalation in people with and without diabetes. Inhalation of the hyperoxic gas mixture caused a statistically significant decrease in arteriolar and venular diameters without altering mean arterial pressure significantly. Arteriolar vasoconstriction in response to the hyperoxic gas mixture was significantly reduced in people with diabetes (3.95% versus 7.75%; p = 0.04), but venular vasoconstriction did not differ significantly. A hypoxic gas mixture caused increased arteriolar and venular diameter and a normoxic,hypercapnic gas mixture had no significant effect on vessel diameter. Responses to hypoxic and normoxic,hypercapnic gas did not differ significantly between diabetes and non-diabetes subjects. Conclusions:, Type 1 diabetes impairs retinal arteriolar responses to hyperoxia. Abnormalities in retinal arteriolar reactivity in response to oxygen may play a role in the development of diabetic retinopathy and this technique may represent a simple means of identifying early abnormalities in the reactivity of retinal arterioles in diabetes. [source]

2424: Pulsatile haemodynamics: potential for end-organ damage?

ACTA OPHTHALMOLOGICA, Issue 2010
C HUDSON
Purpose Increases in velocity pulse wave amplitude, or max:min velocity ratio, represent early haemodynamic disturbances associated with diabetic retinopathy (DR) and age-related macular degeneration. This change reflects an increase in vessel wall rigidity that is generally accepted to occur in the central vasculature but the peripheral vasculature is also implicated in this process. This presentation will highlight the implications of these changes in terms of end-organ damage in DR. Methods The sample comprised 4 groups: Group 1: 50 non-diabetic control subjects. Group 2: 56 diabetic patients without clinically visible DR. Group 3: 54 diabetic patients with micro-aneurysms and / or hard exudates within 2 disc diameters of the fovea in the absence of clinically manifest diabetic macular edema (DME). Group 4: 40 patients with clinically manifest DME. The diabetic patients were predominantly type 2. Retinal hemodynamics were assessed in the superior temporal retinal arteriole using the Canon Laser Blood Flowmeter. Intraocular pressure, blood pressure and relevant systemic markers of diabetes control and complications were also assessed. Results The velocity pulse wave amplitude was elevated with increasing risk of DME (p<0.0001). No significant differences were found between the groups with respect to diameter, velocity or flow. Pulse wave amplitude was correlated to age, duration of diabetes, blood pressure, pulse rate, IOP and serum potassium levels. Conclusion The increase in velocity pulse wave amplitude will induce excessive pressure pulsatility in the retinal arterioles and capillaries, changes in vascular function (e.g. loss of vascular regulation) and changes in vessel structure. Commercial interest [source]

Communication:Dual macroaneurysms on the same retinal arteriole

CLINICAL AND EXPERIMENTAL OPTOMETRY, Issue 2 2005
Mark A DePaola BOptom
ABSTRACT A case of two macroaneurysms on the same retinal arteriole is presented. After observation of these lesions for some weeks, an increased threat to the macula from oedema led to laser photocoagulation. Although treatment did not hasten resolution, the patient has remained asymptomatic. The aetiology and natural history of macroaneurysms are discussed. [source]

Regression of Alterations in Retinal Microcirculation Following Treatment for Arterial Hypertension

JOURNAL OF CLINICAL HYPERTENSION, Issue 8 2006
Antonio Pose-Reino MD
Evaluation of early hypertension-related alterations in retinal microcirculation has been subjective and poorly reproducible. The authors recently described a semiautomatic computerized system for evaluation of the calibre of retinal blood vessels that has shown very good reproducibility. In the study, this system was used to measure the calibres of retinal arterioles and veins, and their ratio, in a group of 51 hypertensive outpatients before and after 6 months of treatment with losartan or, if required for satisfactory blood pressure control, losartan plus hydrochlorothiazide. Mean retinal arteriole diameter increased from 0.0842±0.003 mm to 0.0847±0.003 mm (p=0.001). Arteriovenous ratio increased from 0.753±0.03 to 0.756±0.03 (p=0.005). This observation suggests regression of early hypertension-related alterations in retinal microcirculation after 6 months of antihypertensive treatment. [source]

2421: Wall-to-lumen ratio of retinal vessels in patients with cerebrovascular damage

ACTA OPHTHALMOLOGICA, Issue 2010
G MICHELSON
Purpose There is evidence that generalized retinal arteriolar narrowing, which can be measured by the arteriole-to-venule ratio (AVR) of retinal vessels, predicts cerebrovascular events. The wall-to-lumen ratio (WLR) and wall cross-sectional area (WCSA) of retinal arterioles reflect structural arteriolar parameters. The primary objective was to test the association between WLR and AVR in patients with cerebrovascular damage. Methods In this cross-sectional study, 23 patients (57.5 +/- 9.4 years) with acute transitory ischemic attack or lacunar cerebral infarct were compared with two age-matched control groups: 83 subjects with essential hypertension (53.7 +/- 5.5 years) and 16 normotensive subjects (52.2 +/- 8.3 years). Retinal arteriolar parameters (WLR, WTH, and WCSA) were assessed in vivo with scanning laser Doppler flowmetry (SLDF). AVR and a qualitative evaluation of retinal vessels were obtained from digital retinal color photographs. The intima-media thickness (IMT) of the carotid artery was measured. Results WLR (0.44 +/- 0.1 vs. 0.34 +/- 0.1 vs. 0.30 +/- 0.1, P < 0.001) and carotid IMT (P < 0.05) were significantly greater in the cerebrovascular event group compared with normotensive subjects. WLR and WCSA were significantly higher in the cerebrovascular event group compared with subjects with mild arterial hypertension. AVR was similar in all three study groups. Conclusion The increase in WLR and WCSA of retinal arterioles, as well as in IMT in patients with cerebrovascular damage suggests vascular hypertrophy in the microvascular and macrovascular bed. The lack of association between AVR of retinal vessels and WLR of retinal arterioles [source]

2424: Pulsatile haemodynamics: potential for end-organ damage?

3122: Regulation of retinal tissue oxygenation

ACTA OPHTHALMOLOGICA, Issue 2010
CJ POURNARAS
Purpose To evaluate the changes in the retinal oxygen partial pressure (PO2) following physiological stimuli. Methods Evaluation of either the preretinal and intraretina partial pressure of oxygen (PO2) distribution, using oxygen sensitive microelectrodes, in various animal models. Measurements were obtained during changes of the perfusion pressure, systemic hyperoxia, hypoxia, hypercapnia, carbogen breathing and following carbonic anydrase inhibitors use. Results The oxygen tension (PO2) in the inner half of the retina remains largely unaffected by moderate changes in perfusion pressure. The increase of the systemic PaO2 through breathing of 100% O2 (hyperoxia) induces endothelin (ET) mediated marked vasoconstriction of the inner retinal arterioles in both anesthetized animals and normal human subjects. The regulatory vasoconstriction maintains the PO2 in retinal tissue constant. A decrease in PaO2 (hypoxia) induces a vasodilation of the retinal arterioles through endothelium-derived NO release. As a result, trans-retinal PO2 profiles made during steps of systemic hypoxia have shown that the values measured in the inner retina up to half of its thickness, remain rather stable. By contrast, the PO2 values, measured close to the choroid and in the outer retina, decrease in a linear manner with the decrease of the PaO2. An increase in the PaCO2 (hypercapnia) of arteriolar blood, produces an increase in retinal blood flow and retinal tissue PO2. Intravenous injection of acetazolamide (carbonic anhydrase inhibitor) produces an increase in preretinal PO2 due to dilation of the retinal vessels Conclusion Thanks to the autoregulatory capability of the retinal circulation, the oxygen tension (PO2) in the inner half of the retina, remains largely unaffected during physiological stimuli. [source]

3123: Non-invasive measurement of retinal oxygenation: principles and expectations

ACTA OPHTHALMOLOGICA, Issue 2010
M HAMMER
Purpose To determine oxygen saturation (SO2) of blood inside retinal vessels which is an essential measure for the estimation of oxygen supply to the tissue as well as its oxygen consumption. Methods Two-, four-, and multiple - wavelength approaches to the non-invasive measurement of SO2 will be discussed. The dual wavelength technique, imaging the fundus at 548 and 610 nm, showed to be most appropriate for clinical routine investigations. The SO2 of the hemoglobin in retinal arterioles and venules is calculated from the ratio of the optical densities of the vessels at both wavelengths. Results From a healthy control population, mean arterial and venous SO2 were measured to be 98±10.1% and 65±11.7% with reproducibility of 2.52% and 3.25% respectively. In a cohort of 41 patients (mean age: 65±12.3 years) with diabetic retinopathy (DR), we found an increase of the venous SO2 with the severity of DR: Mild non-proliferative DR 69±7%, moderate non-proliferative DR 70±5%, severe non-proliferative DR, 75±5%, and proliferative DR 75±8%. Measurements of SO2 in accordance with vessel diameters revealed a correlation of the venous SO2 with arterial as well as venous diameters in 159 diabetic patients (mean age: 55.8±13.9 years) with no or non , proliferative DR. Increased venous SO2 is an indicator of insufficient oxygen supply to the retinal tissue. The correlation of the vessel diameters with venous SO2 may point to compensatory mechanisms of retinal blood flow regulation. Conclusion Accurate retinal vessel oximetry is possible by non , invasive optical methods. Combined with measurements characterising the retinal blood flow, it is a powerful tool for the estimation of retinal oxygen supply and consumption. Commercial interest [source]

Retinal arterioles have impaired reactivity to hyperoxia in type 1 diabetes

Retinal oxygenation in diabetic retinopathy

ACTA OPHTHALMOLOGICA, Issue 2009
SH HARDARSON
Purpose Diabetic retinopathy (DR) is believed to cause retinal tissue hypoxia by damaging retinal capillaries. The purpose of this study was to examine the effect of diabetic retinopathy on oxygen saturation in retinal arterioles and venules. Methods The retinal oximeter (Oxymap ehf., Reykjavik, Iceland) is composed of a fundus camera, beam splitter and light filters. Specialized software calculates relative oxygen saturation from light absorption at two wavelengths of light (605nm and 586nm). One first or second degree temporal arteriole and venule were measured in one eye of 31 healthy individual and 28 patients with diabetic retinopathy. The diabetic patients had background DR (n=6), macular oedema (n=7), untreated preproliferative or proliferative DR (n=7) or stable proliferative DR after treatment (n=8). Statistical analyses were performed with an unpaired t-test, one-way ANOVA and Dunnett's post test. Results Retinal arteriolar saturation was 93±4% (n=31, mean±SD) in healthy subjects and 101±6% (n=28) in patients with DR (p<0.0001). Retinal venular saturation was 58±6% in healthy subjects and 67±8% in diabetic patients (p<0.0001). Arteriolar and venular saturation was higher in all subgroups of diabetic patients (see methods) than in healthy subjects. Conclusion Increased oxygen saturation in retinal vessels in diabetic retinopathy, also found by other researchers, is consistent with poor distribution of blood and oxygen to the retinal tissue rather than decreased total retinal blood flow. Poor distribution of oxygen may be caused by capillary dropouts and shunts as well as thickening of the capillary walls. Commercial interest [source]

Noninvasive oximetry and glaucoma

ACTA OPHTHALMOLOGICA, Issue 2009
OB OLAFSDOTTIR
Purpose To investigate retinal vessel oxygen saturation in relation to glaucomatous visual field damage. Specifically, we examined whether oxygen saturation in retinal blood vessels differs between regions corresponding to glaucomatous visual field defects compared to regions without visual field defects. Methods A spectrophotometric retinal oximeter (Oxymap ehf, Reykjavík, Iceland) was used to measure oxygen saturation in retinal arterioles and venules. The oximeter consists of a fundus camera, beam splitter, light filters and software that evaluate the oxygen saturation. The glaucomatous defect was estimated from a visual field test using the Octopus 1-2-3 perimeter. One eye in 13 individuals with open angle glaucoma with or without pseudoexfoliation syndrome was examined. Results In retinal areas with no visual field defect, the mean oxygen saturation in arterioles was 102±6% and 65±9%, (mean±SD) in venules. The arteriovenous difference was 37±10%. In retinal areas corresponding to visual field defects, the mean oxygen saturation in arterioles was significantly lower; 98±5% (p=0.04, paired t-test, n=13). The venules were at 68±7% (p=0.3) and the arteriovenous difference was also significantly lower; 30±10% (p=0.04). Conclusion Arteriolar oxygen saturation and arteriovenous difference is statistically lower in areas with visual field defects compared to areas without visual field defects. This data suggests that visual field defects are associated with a reduction in retinal oxygen delivery and metabolism. [source]

Response of retinal arteriole diameter to increased blood pressure during acute hyperglycaemia

ACTA OPHTHALMOLOGICA, Issue 3 2007
Peter Jeppesen
Abstract. Purpose:, To study retinal response in terms of arteriole diameter and retinal thickness secondary to an increase in arterial blood pressure during acute hyperglycaemia. Methods:, In a randomized, double-blinded, cross-over study, nine healthy persons were subjected to clamping of blood glucose to either 5 mmol/l or 15 mmol/l using somatostatin to control endogenous insulin secretion. The response of retinal arterioles in terms of diameter as determined with the retinal vessel analyser (RVA) and retinal thickness as assessed by optical coherence tomography (OCT) were measured after an increase in arterial blood pressure induced by isometric exercise. Arterial feeding pressure in the eye was assessed from the ophthalmic artery pressure and pulse amplitude measured by ophthalmodynamometry. Results:, Isometric exercise induced a significant increase in mean arterial blood pressure and a significant contraction of the retinal arterioles. An acute increase in blood glucose from 5 mmol/l to 15 mmol/l did not affect either the diameter of retinal vessels or retinal thickness. Conclusions:, Acute hyperglycaemia per se does not change isometric exercise-induced retinal arteriolar contraction. Metabolic factors other than blood glucose are suspected to be involved in the impairment of retinal autoregulation as seen in hyperglycaemia induced by oral glucose intake. [source]